This invention relates to the general field of power generation systems, and more particularly to an improved power generation system for a hybrid electric vehicle (HEV).
Electric vehicles powered by storage batteries are subject to inconvenient energy replacement procedures. One of two procedures are currently used; either replacing the discharged battery with a fully charged battery or connecting a source of charging power to the vehicle and allowing the vehicle to sit, out of service, while the charging process is completed. Another operational disadvantage of a conventional battery powered electric vehicle is its inherent range limitation.
The hybrid electric vehicle is an attempt to overcome the above limitations. The usual way to form a hybrid electric has been to add an engine-generator to the electric vehicle for the purpose of battery charging while the vehicle is in operation. The conventional engine-generator has been of the reciprocating internal combustion configuration and the engine fuels have included diesel, LNG, CNG, propane, among others.
While the addition of a conventional internal combustion engine does solve the problems of charging and range, it introduced several significant disadvantages, including the vibration and noise caused by the reciprocating engine. More significantly, however, was the disadvantage of the air pollution caused by the burning of the hydrocarbon fuels in the reciprocating engine. The combined effects of noise, vibration, and air pollution renders the hybrid electric vehicle with a reciprocating engine less than ideal.
In addition, the output or bus voltage of the reciprocating internal combustion engine generator varies with the speed of the engine. This requires that the engine speed must be closely regulated to control the output or bus voltage with the consequence that the engine cannot be run too low in speed else the bus voltage would not be high enough to generate some of the voltages that are required. Contemporary HEV systems utilize battery voltages ranging from 250 V to 600 V, making it difficult to match the engine to the vehicle battery voltage. As a result, the engine needs to be run at higher speeds and lower temperatures, making it less efficient.
What is needed is an electric vehicle power system that overcomes the limitations described above.
The invention is directed to a hybrid electric vehicle, such as a bus or delivery vehicle, which includes batteries and a turbogenerator/motor connected through a bi-directional double conversion control system. The batteries and the turbogenerator/motor are each connected to a DC bus through bi-directional power converters operating as customized bi-directional switching converters configured, under the control of a power controller, to provide an interface between the DC bus and the batteries and turbogenerator/motor, respectively. In this manner a wide range of HEV battery voltages can be accommodated and also permits the HEV battery voltages to be used for starting the turbogenerator/motor.